Not necessarily. When you live inside the wavefunction the outcomes of certain experiments very much look like a wavefunction collapse. MWI is a way to explain

Not necessarily. When you live inside the wavefunction the outcomes of certain experiments very much look like a wavefunction collapse. MWI is a way to explain why that happens without having to have a special case where the universe has a completely different behaviour for just a moment in time. You can formalise the mathematics of it using the concept of quantum decoherence.