If by 'guessing' you mean writing down numbers that you are not sure about, then no, every puzzle is solvable (in theory) by looking at all the possibilities remaining. This is the brute force algorithm.

However, some puzzles are complicated enough that you won't be able to remember all the possible values. This is simply a case of humans having poor short-term memory, and you will require additional resources (like writing down numbers and trying them).

As you get better and better at solving Sudoku puzzles, your brain recognizes more and more patterns, and when the puzzle you're solving matches one of those patterns, your brain can remember the solution. The more experience you have, the less difficult your reasoning becomes, and the less likely you are to find a puzzle that requires brute forcing.

If by 'guessing' you mean writing down numbers that you are not sure about, then no, every proper puzzle is solvable (in theory) by looking at all the possibilities remaining. This is the brute force algorithm.

However, some puzzles are complicated enough that you won't be able to remember all the possible values. This is simply a case of humans having poor short-term memory, and you will require additional resources (like writing down numbers and trying them).

As you get better and better at solving Sudoku puzzles, your brain recognizes more and more patterns, and when the puzzle you're solving matches one of those patterns, your brain can remember the solution. The more experience you have, the less difficult your reasoning becomes, and the less likely you are to find a puzzle that requires brute forcing.

If by 'guessing' you mean writing down numbers that you are not sure about, then no, every puzzle is solvable (in theory) by looking at all the possibilities remaining. This is the brute force algorithm.

However, some puzzles are complicated enough that you won't be able to remember all the possible values. This is simply a case of humans having poor short-term memory, and you will require additional resources (like writing down numbers and trying them).

If by 'guessing' you mean writing down numbers that you are not sure about, then no, every puzzle is solvable (in theory) by looking at all the possibilities remaining. This is the brute force algorithm.

However, some puzzles are complicated enough that you won't be able to remember all the possible values. This is simply a case of humans having poor short-term memory, and you will require additional resources (like writing down numbers and trying them).

As you get better and better at solving Sudoku puzzles, your brain recognizes more and more patterns, and when the puzzle you're solving matches one of those patterns, your brain can remember the solution. The more experience you have, the less difficult your reasoning becomes, and the less likely you are to find a puzzle that requires brute forcing.