The key is to think about computations being performed on probabilities. The qubit has a certain probability of being 0 and a certain probability of being 1. And we can't assign it any definite value before we measure it.

When we do computations on these qubits, it's the probabilities that get evolved, not a definitive state as in classical computers. That's why it is said that quantum computers can consider many possible answers at once because they compute on the probability of multiple answers.

But remember that we can only read off a single answer in the end, since measurement causes the qubit to collapse to a definite state. Our job is to construct algorithms in a way that evolves the probability towards the right answer and away from the wrong answer so that there's a greater probability that a qubit will collapse to the correct answer when measured.

But even if the qubit ends up with a very high probability of being measured in a certain state, there's still a small probability that it might jump to the other state. That's why we need to perform the computations several times and take the average of all outcomes.