LL(1) and LR(0) Grammars
The question to be answered in an $LR(k)$ parse is "has the parse reached the end of a production?" (And if so, which production?)

If we are at the end of a production, we choose a reduce action. Otherwise, we shift the next input whatever it is.

So it should be clear that there are grammars which can be parsed without any lookahead; they are grammars in which no right-hand side is a prefix of a different right-hand side.