This lesson focuses on common English grammar mistakes, specifically the incorrect ordering of binomial pairs—fixed word pairs always used in a specific order. Examples include 'salt and pepper' (never 'pepper and salt'), 'bread and butter', 'knife and fork', 'cup and saucer', and 'thunder and lightning'. While using the reversed order might be understood, it's grammatically incorrect and should be avoided to maintain proper English usage. The video uses these examples to highlight the importance of respecting the fixed order of these word pairs.