C exposes a lot of things, and also hides a lot of things about the underlying system that can get confusing. What's an "int"? Or a "long" You need to know for your platform what the bit width is on your platform, because it's not explicit in the name, and the language is willing to do a bunch of implicit stuff behind the scenes with only a warning or two. Should you really be using 'char'? Is yours a legit use of it or did you mean uint8_t? Other high level languages generally tend to have more sensible default patterns for these things, C ... it gives you all kinds of ammo to shoot yourself with.

It's not as big of a problem these days with things becoming less heterogeneous; almost everything is little endian now, much of it 64-bit but at least 32-bit, and we can kind of rely on POSIX being there most of the time. Most new code uses stdint.h and is explicit about word lengths by using int32_t, etc. and follows good conventions there.

But venture off the beaten path into odd microcontrollers or into retro machines or port older code or whatever ... and there's glass hidden in the grass all over.

C also exposes a model of the machine that looks low level but behind the scenes a modern processor does all sorts of branch prediction and pipelining and so on that can blow up your assumptions.

What looks like optimized clever C code can actually end up running really slow on a modern machine, and vice versa.