Probability after the event A friend of mine says that you can't calculate the probability of an event after it has happened. The reason for that is that it has a probability of 100% for the event has occurred.
Secondly he states that any event is highly improbable, say me writing this email, if one takes into account background information such as my language, that I should chance upon this website, that you should choose to answer this question etc. When construed like that the odds become astronomical, and for this reason every event that has taken place is highly unlikely?
Please help resolve my confusion.  
 A: The statement "the probability of event $E$ is $p$" can be taken as shorthand for "a certain specific probabilistic model  assigns probability $p$ to the event $E$." The truth of this does not depend on whether or not the event $E$ has happened.
A: The probability of an event is always relative to information about the event known when the probability is calculated. As the information changes, so does the probability. Often, the information evolves from very little, which may correspond to a low probability, to complete information about the event---say, that it has happened, or cannot happen, corresponding to to a probability of $1$ or $0$.
A: The second statement of his contradicts his first.
Probability of an event that has occurred can still be done, for example, if you role a dice, it has a 1/6 probability of landing on any number, after it has landed on a two, you can still calculate the probability of it occurring to be 1/6. The probability that you had rolled a two is 100%, as you did roll a two. The probability that I won the lotto was not 100% after the fact, it was still very, very low.
The probability that you complete every action up to this point in such a specific way isn't even a matter of probability, as everything that physically altered your path was bound to happen, taking into account the function of excitatory and inhibitory neural pathways, I could argue that biologically there was no element of decision that cannot be physically explained.
