To preclude something is to make it impossible before it can happen — to shut the door in advance. A knee injury precluded a career in football: the injury did not just discourage the career, it closed off the possibility. This is a formal word, at home in law, official rules, academic writing and careful journalism. The pattern to learn is 'X precludes Y' or 'X precludes someone from doing Y', where X is usually a rule, a fact or a condition rather than a person choosing. So 'the contract precludes us from selling the data' is natural; 'my brother precluded me from going' is not — you would say 'stopped me'. One very common use is to say two things can both be true: 'accepting the offer does not preclude looking for other work.' That negative form, 'does not preclude', is probably where you will meet it most, and it means 'still leaves it possible'. Compare 'prevent', which is the everyday word and can describe stopping something already under way; preclude is about the possibility itself, decided beforehand.