TYPICAL ERROR The decision about which course to do of the many possible ones at so many different institutions, is only the first hurdle. The fact is, there are also all the social activities you have to learn how to cope with.
CORRECTION The decision about which course to do of the many possible ones at so many different institutions is only the first hurdle. The fact is that there are also all the social activities you have to learn how to cope with.
EXPLANATION A short-hand rule for commas is that we insert them in a sentence where we would pause if we were speaking the sentence aloud. While generally okay, this 'rule' can sometimes cause errors. Sometimes when we speak, we pause in places where a comma should never be used in written language. One of these places is between a subject and its verb. If you are speaking, you may need to pause to take a breath after a very long subject but you should never put a comma there if writing the sentence.
Another situation where we do need to pause when speaking is when we leave out the word that after the verb, as in:
That sentence actually is:
When we leave out words such as that, they are said to be 'understood' by the audience. That is okay when we are speaking, but when we write - and especially in formal writing - the meaning is clearer if we use full grammatical structures, so it is better to insert that than to replace it with a comma.