Could someone ELI5 what it means when it is said that a miner needs to hash the block’s header in such a way that it is less than or equal to the target?

In particular the 'less than' part. Why is not just equal to? I realize this is a dumb question but I'm struggling.

If we think about it as trying to guess a number between one and ten, and the target is 3 but the answer can be less than or equal to 3 (and everyone knows this) wouldn't everyone guess the lowest number (0 or 1)? I'm very confused about this and have not had any luck finding an easy to understand answer.

Thank you in advance for any help.

Edit: These answers are great, I won't go replying to each one but just wanted to say thanks to all who have responded. I think I'm starting to get it at last.

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