Since people have asked and whatnot, magical resistance specifics incoming. Yes, this is how it work in canon but sunk down into layman's language.
Magical resistance confers magical resistance/immunity depending on rank against magical attacks that attack the servant directly. That includes blasts both large and small along with large area magic attacks. It, however, does not apply to a number of other things which include magic that makes things. Summon magic (like zero caster's tentacle monsters of doom), tracing (like Shirou's traced swords), and so forth fall under this category. This does not mean that a tracer has any greater capability to hurt a servant than usual given that the average servant is so far physically superior but it does mean that tracing gets around magical resistance and whatnot. Reinforcement magic also bypasses it as it targets a third part object (like fists or a weapon), not the servant that its ultimately going to smack. However, reinforcing a servant with high magical resistance probably will not work that well. Feel free to figure out other ways around it or ask if you're not sure. They do exist.
I don't really anticipate this to be a problem since its mostly Caster using magic (and said Caster already knows this better than I do I'm sure) and the various masters who would generally be steamrolled by any given servant that isn't dying and prana deprived. But there are cases in which it matters so I leave this note here.
