The right dumbbell choice is not only about whether you can move the first repetition. Consider the full set, the setup, and how you will return the weights safely. Use resistance appropriate to your experience and the exercise. A manageable pair lets you practice the intended movement rather than inventing momentum to finish what you started.
Check labels and confirm that the two dumbbells match when the exercise calls for a pair. Keep the surrounding floor clear. Learn safe positioning and transitions with qualified instruction if the movement is unfamiliar. Do not assume that a weight you use in one exercise will be suitable in another simply because the same implement is involved.
Observe later repetitions and the end of the set. If control changes substantially, note that context. Avoid treating every completed motion as identical work regardless of technique. Pain or an uncertain setup calls for stopping and reassessing, not simply choosing a more determined expression. Appropriate guidance can help you decide what adjustment is useful.
Record the exercise variation and working weight clearly. At the next session, use the record as information rather than a command to increase automatically. A consistent, controlled set provides a better basis for progress than a larger number achieved through a different movement. Choose the pair that serves the task you actually intend to practice.