What I typically tell people is "solder will stick to the part that melts it." If you melt the solder with the iron tip, it will stick to the iron. If you use t

What I typically tell people is "solder will stick to the part that melts it." If you melt the solder with the iron tip, it will stick to the iron. If you use the iron tip to heat the joint and melt the solder with the joint, it will stick to the joint. The physics isn't correct but it's served me well as an easily remembered rule-of-thumb.