Why is the play in two acts?

Consider the idea that these characters are simply mirroring one another, doing "something" yet doing nothing. The two acts show different sides of the same character, but their "waiting" is quite symbolic. Consider that their lack of movement and the absurdity of their situation teaches us something about life and how absurd it can be.

from my point of view.  the writer wants to show us that life and nature are changeable.but human beings caused their life un changeable! !!! they suffer because of their mistakes and silence towrds life . and I can prove that by act 2 that the tree has leaves. and pozzo became blind and so on . here we can see the power of nature and it's movement unlike human beings.   Hemn .n.mohemmed

The fact that Act 2 is quite similar to Act 1 - the characters continue living life basically just the way they do in Act 1 - predicts that they will do the same if there was Act 3. Act 3, therefore, I think is unnecessary because readers can assume that the characters would do the same things and repeat the cycle of life that they are living. For the message that the playwright wants to deliver through the play, 2 Acts are sufficient, unless there was any big change to take place. But, the fact that Act2 ends just the way the play has started also insinuates that there is definitely no change going to take place.

I think, the reason behind that is to show uniformitarianism of the characters and the situations happening in the play. Beckett wanted to convey the idea of absurdity in an authentic way from every aspect. So, he presented two acts also to show that this nonsense attitude will last longer.