it’s also worth mentioning this is the reason even though the compiler/linker shows - say 80% memory utilisation, that number doesn’t account for transient use of memory by passed values, heap and stack usage.
it’s very common that even 10% free ‘memory’ is not enough. It all depends on how you toss the memory around within your code. e.g. globals and statics are convenient, but use permanent memory allocation.
If your sketch crashes or behaves oddly... apart from coding bugs, go looking for RAM optimisation to get that utilisation down as much as practical.