In the mind of an English speaker, there's a clear difference between talking
about an event that happened in the past and talking about
something that has happened. The difference is whether there's
an effect on the speaker right now.
For example, if you
say "I ate" it's just a fact - you ate at some time in the past. It doesn't have
any connection to how you feel right now.
But if you say "I've eaten",
that expresses