I grew up in southern Germany, speaking the local dialect. As a young adult, I thought I could speak accent free German. I couldn't have been more wrong. Many people in Hamburg and Berlin rightfully guessed that I'm from Bavaria. Closely related languages and dialects exist in a continuum ((Max Weinreich: "a language is a dialect with an army an a navy"). Many people in Ukraine spoke and speak "surzhyk", depending on the political climate, they could claim to speak Russian or Ukrainian. Then Russian and Ukrainian, together with Belarusian form a dialect continuum. You can easily understand you neighboring village, but it gets harder and harder, the further you are apart until there's very little mutual intelligibility.