Andrew Ellington gives to his undergraduates upon entering his research laboratory. I altered them slightly in my recent words of advice to a cohort of freshmen at the start of their college careers. The punch line (that is the one that gets the laugh) is "don't die" and that one I definitely kept. It's funny because it echoes the fear many of us have in entering a laboratory. There's real danger there because solutions can spill, equipment can break and chemical reactions can go awry in all sorts of ways. There's also psychic danger because there's the possibility that old dogmas will be shattered by your findings. Both of these require a bit of safety training and a prepared mind.
Students can't allow themselves to be paralyzed by the fear of making some mistake, small or large in a laboratory. In order to motivate my students to move forward, I encourage them to summarize ALL their findings during our meetings, not just the ones that "worked." After all, the ones that didn't work may be just as instructive. If nothing else, a listing of all the failed (numerical) experiments shows me that they were busy doing something useful. The important thing is to understand a given experiment didn't work, at least in hindsight. If you can't explain it based on known theory, then there's the possibility that something new has come about. Doing this level of analysis, not included in the title's advice, is what makes the exploration done in the lab a science.