I couldn't possibly fit my entire arguement into this one post. So ill just ramble a little while and see what comes up.
Aside from the fact that you are usually closing yourself off to a variety of amazing experiences, I find one of the largest problems with knowing is that you might end up repeating the same "mistakes" over and over again. When we know, we are certain, and for most people certainty gives life to purpose. What we attach to that purpose can be a lot of things but ultimately it leaves very little room for us to explore what's possible.
I often tell my self and my friends "I don't know is a great place to start" because often times when we are sure it causes a lot of stress and pressure. We set up expectations, on others, the world, and most of all ourselves. I'm coming up on my 30th trip around the sun and find a bit of comfort that I just don't know about a lot of things. Its taken me a long time to get comfortable in the void and hope to stay here for a hot minute. Just taking it in as it comes or as a great friend of mine says "I've got a 4 day buffer".
There are somethings I do know...
And to me that's another great place to start. Know what makes you happy, sustains your happiness, and jump off that cliff to get it. If mid way through the free fall you start to doubt that this choice in some way shape or form bring you to a higher plain of existense, I urge you to think again, and occasionally check in with your intentions. Come from the heart friends and see how you are rewarded through out this grand master narrative.
I'm not making a case for ignorance and I definitely hope those reading this don't assume apathy is the way togo. I guess I'm pleading you to stop, let g, and see what life has to say. :D