Sometimes, Spock would really get it handed to him -- never more so than in "The Galileo Seven," the episode where Spock is in command of a shuttlecraft on a scientific mission and ends up marooned on a hostile planet. He attempts to deal with the situation entirely on the basis of logic, which leads to rather strong confrontations with McCoy and another science-department officer on board. Spock's "logicial" actions lead to the deaths of two crewmen (remarkably wearing gold shirts, not red), and in the end, he abandons logic completely and goes with a gut instinct which leads to a successful rescue. The high point in the episode is a moment toward the end where Spock is mumbling to himself about how he's followed every logical course and made every decision based on logic -- and yet he's failed. Impressive acting by Nimoy here, and a defining moment for Spock in realizing that even he isn't right all the time.