Learn Croatian: Uzrok i posljedica nisu isto. - Cause and consequence are not the same.

Here, isto acts as an abstract noun meaning "the same thing", rather than an adjective modifying the subjects. If you used the plural adjective isti, it would sound like you are saying the two items don't physically look identical. Using isto expresses that they are fundamentally not the same concept.

What is the difference between uzrok and razlog?

While both can translate to "cause" or "reason" in English, uzrok usually refers to an objective, physical cause (like the cause of an accident, fire, or illness). Razlog is a "reason" or motive, which involves human thought, intention, or justification (like the reason you were late).

How can I easily remember the word posljedica?

Look at its root! It is related to the verb slijediti (to follow) and the noun slijed (sequence). With the prefix po- (meaning after), posljedica literally translates to "that which follows after" — which is exactly what a consequence is.

Why do we use the plural verb nisu if isto is singular?