Many of the most crucial events in our lives are predestined by physiology, traditions and culture, the general properties of time, space and matter and many other non-variables. However, there is always the element of surprise or 'freedom of choice' in life. There is always the small element of freedom or the non-predestined part that does make our lives so interesting and also worth living.
Some of us will get cancer and quite similar people will not. Some of us will wind up under a bus and most of the others will not. Some of us will learn from our mistakes, but most of us will not, but keep on repeating them.
Some of us will find the love of their life, but others will not. Some of us will be happy with they have already got, but others will complain until they die. Some of us will be happy, and others will not be under quite similar circumstances.

One could say that a lifeless world is also a predestined world. The ‘laws of nature’ or the basic structure of the physical world will govern it. A planet or sun will go through a process of birth and decay that can well be almost totally predicted.
However, the birth of life makes things much more complicated. Every living thing has an ability to act also unpredictably. This ability grows with the complexity and most of all with growing abilities of evolving life-forms.

The most basic and simple life-forms do lead quite predictable lives, but the level of predictability is eroded with the rise in complexity of life. The introduction of life-forms that have the ability to change their environment will inevitably make systems less and less predictable. However, unpredictable life can exist also in a quite predictable environment.
Even most of the actions of life-forms in the planet Earth can be predicted to a degree. However, the existence of self-propelled life will eventually erode the predictability of a system, even if it will never go away completely. To what degree this happens varies wildly in different situations and environments.

Wikipedia

The problem is that many people want to categorize a so vast and multi-faced phenomena as life in one single category of "predestined" or "free". However, in reality life is always a combination of both. The amount of how predestined things are or how free we are to choose varies immensely from situation to situation, day to day and place to place.
Of course, also the level of zoom is an important thing here. If you look too close on an event in human life, you will lose the big picture of causes and consequences that are behind the event. However, if you look from too far, you will lose sight of all of the little things that can lead to a bigger event in the life.

The biggest obstacle for understanding the true nature of life as a combination of predestined and 'free to choose' elements is the false dichotomy in which things are classed just as either predestined or ‘totally free'. In the real world, most things are combinations of these two. The level of freedom of choice can vary wildly with time even on same issues with time.
An event can be 0,01 per cent predestined and 99,99 per cent free or in the other end it can be 99,99 per cent predestined and 0,001 per cent free or anything in between. They are mostly in between. However, many people claim for no apparent reason that there are just two choices – things are either totally predetermined or totally free. They forget totally that real life is not at all like that. Outcomes in the real world are always combinations of many kinds of different, simultaneous forces.

The idea of total predestination or total freedom of choice can be valid only in a vacuum of a theoretical world. Unfortunately, many people choose to spend their time in the vacuum of a theoretical world...
The freedom of choice is in one sense a variable that can also be traded or bought and sold. This aspect just cannot be left out from when one considers if a human life is predestined or not. This is naturally somewhat different idea than predestination and fatalism that can grow out of it. However, in the real world the needs and will of other people are even the main reason why we do certain actions and make many decisions.

Of course, one can claim that these needs are predestined, but the same holds true to them as life in general. Most of these needs are generated by previous events and are in this sense predestined.
However, there inevitably remains the element of chance and freedom of choice even here. A person will give away much of my freedom of choice to achieve benefits that are offered by social institutions like marriage and membership of a society.

Most of all a person will sell much of freedom of choice in exchange for food and shelter from elements that is when he or she sells the ability to work to others. The buyers can and will then demand sellers to diminish their own freedom of choice to satisfy the needs of the buyers of the work.
All in all, life is not predestined or free. It is an ever-chancing combination of both. The exact amount of predestination or freedom of choice varies immensely from issue to issue and day to day.

Sam Harris has recently published a book called "Free will" on this subject. It is  a worthwhile read on the subject of predetermination and freedom of choice. However, he has slipped too much to the deterministic camp because of some his very basic views of how human mind works.
Sam Harris claims that the fact that we can see how an action emerges from the human mind before we are even aware of it in a conscious level is some kind of proof for a deterministic world. However, subconsciousness is an integral and important part of human cognition. Subconscious mind is, in fact, the place where all the big decisions are prepared before they are brought to a conscious level.

One's whole life-experience, inherited genetic properties and learned cultural traits all take part in the process of subconscious decision-making before the process ever surfaces to the conscious level. However, it is YOU who is making these decisions in the subconscious level, even if you are still not aware of it in a conscious level.

(This piece was refurbished on 4th of June, 2013)