Why can't Democrats just wait for a filibuster to end?

I am NOT trying to start a political debate - this is just a question I have never heard an answer to. There is a lot of talk about why the democrats need 60 votes to overcome a filibuster. My understanding is that a filibuster is when one party can prevent a bill from going to the floor for a vote by talking for a long time. Is there an actual reason why the Democrats can't just say "OK, go ahead and talk," and wait for Republicans to get tired and yield the floor? It's not like they can talk forever... a few days/weeks max.