What is the single biggest mistake in Spider?

Filling an empty column without a plan. Empty columns are the only place you can take a mixed run apart, and giving one up for a small tidy-up is how a winnable game locks up.

Should I always deal when I run out of moves?

You have no choice at that point, but the mistake happens earlier. Before you get stuck, take every move available — a deal buries options, and moves you skipped may not come back.

Is four-suit Spider actually winnable?

Yes, but typical win rates are 5–15% even for good players, against 80–90% at one suit. A low win rate is expected rather than a sign you are playing badly. Building in suit and protecting empty columns matter far more at four suits than at one.

Does it help to memorise where cards are?

Less than in Klondike, because two decks mean duplicates and five deals keep changing the table. Position and structure matter more than recall — keep runs movable and columns short.

Spider Solitaire Strategy — How to Win More Often

Spider Solitaire StrategyThe decisions that actually change your Spider win rate: turning cards over, guarding empty columns, building in suit, and when to take the deal.