The world is full of change. Plants grow. People age. The Earth rotates. And yet there are philosophers like Parmenides who denied that anything like change can happen due to the metaphysical puzzles that surround it. One such puzzle can be stated as follows:
If object A changed from moment to moment, then object A ceases to exist. If something changes, then it isn't the same. To say that a house underwent change — burning to the ground — is to say, in some important sense, that the house ceased to exist due to change.
On the other hand, if object A doesn't persist from moment to moment, then how could it undergo change? An object that ceases to exist over a few moments doesn't exist, and so cannot undergo change, e.g., to say that David grew a foot over the last year is to say that someone — the same person — changed in height over time.
How is change possible? Many philosophers have offered solutions, and yet the problem is perhaps the most central puzzle in the whole of metaphysics.