system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What exactly was the benefit of dodos and other flightless island birds losing the ability to fly due to a lack of predators?

I know that they lost the ability to fly since they had no predators on land, but why? What benefits did they get by being unable to fly? I see no clear benefits.
gpt
For evolution to happen, there does not necessarily have to be an advantage. The only thing that is more or less necessary is that new/lost features do not have a real disadvantage.

You can compare it to the evolutionary predecessers of humans losing their tails over time: If you don't use it, it's not really a big deal if you lose it. 

So, if these birds don't use the wings, mistakes will go (almost) unnoticed. These mistakes will accumulate over time and eventually, the wings will be 'broken beyond repair' and you're a dodo. 

Same thing happens with fish in very dark waters, they've often lost their eyesight over time.