Sometimes we meet people, with whom we fell so confident and so natural, as we know them for a long time. With those people you can be yourself and forget about all problems. Sometimes we meet people, by talking to them for a couple of a minute, we feel as we know them for years and even spend pleasure time with them. By experiencing those feelings, you can not find any logical explanation. So somebody may explain that by destiny (like they were born for each other), somebody by genetics, and others by beeing together in other life or at the parallel Universe... Actually, I believe in the love at first sight, but I don't know why it happens. I don't think that factors like similarity in interests, being in the same situation, in the same "ship" and others may explain this. All of those are only options and not main cause. The main cause is very deep.
In addition, that first feelings are not always reliable and not always true