[mr_toad]

Languages (parsers and interpreters) aren't that hard to design. People do it for fun (e.g. Brainfuck or Whitespace). Good compilers are much harder.

[kzrdude]

Rusts borrow checker, ownership and whole model is quite complicated actually. Remember we are going for a complete, sound model without holes.

There have been soundness bugs during development and I think we have some really amazing people behind the core language that have been able to refine and adapt rust as it grows.