To lead means to guide someone or something (usually by holding a hand, halter, rope, etc.) or to be in charge of something or someone. "I will lead you through the darkness" or "I will lead the team to victory." So to lead requires some sort of participation on the part of the person who leads. To trigger means to cause something to happen or occur. "His rude remark triggered her anger" or "If you go to her house, her cats will trigger your allergy." Or "the smell of crayons triggers memories of childhood." The outcome happens as a reaction to the trigger.