Why do we need proof of work? Why not have it the first transaction that gets recognized becomes the only one valid?

I don't think that answers my question, or is that is far too simplistic of an answer for me to understand.

When I first learned about how the blockchain works, how mining provided proof of work and prevented someone from putting fake blocks or transactions on the blockchain, it works perfectly and makes sense.

However, when I try and compare blockchain vs a system in which multiple nodes are listening to each other, as soon as one node receives and accepts a transaction, any others that are of some address giving to another without that person having the funds gets thrown out, is what confuses me.

Basically what I am asking is, what are the drawbacks to the type of system I am asking about here. I know there are some I just can't think of them.

/r/Bitcoin Thread Parent