Whisking your eggs until no white streaks are left is a bad idea. For fluffy, cohesive scrambled eggs, only beat the eggs until they are combined to avoid a tough, rubbery mixture.
Only whisking the eggs until they're combined ensures that their enzymes are still connected. Over-whisking breaks up the eggs, creating dry, detached bits that aren't as tasty.
Whisk the eggs only until air enters the mixture to ensure they're fluffy. This might mean scrambling eggs with a fork instead of a whisk to avoid over-scrambling.