To avoid a guess, learn a key fact

Sherlock Holmes said, "I never guess. It is a capital mistake to theorize before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts."

That definitely applies to some bridge players. They make an assumption about the lie of the cards that proves to be inaccurate. Then they complain they were unlucky, when they could have played differently to uncover the critical fact.

How does that apply in this deal? West leads the spade king against three no-trump.