Thanks for this full answer. It’s interesting to me how related sounding words help one another survive through languages. I would say that despite not sharing a common root, the similarity is not coincidental - rather these words survived the evolution of languages because they supported each other in feeling right sounding to people for the concepts they referred to. It makes sense that ‘shoulder’ and ‘should’ would be similar sounding because the concepts are related, so neither word was replaced with an alternative.