A natural result comes from clean sections, even tension, and a placement that moves with the head.
Too close to the scalp
If the weft is attached with no room to move, pressure can build up. Keep about 0.5 cm of distance and check that the row moves comfortably.
Uneven tension
Individual points under too much tension can pull. Section your own hair evenly and check every bead before moving on.
Too high or too close to the hairline
Allow for enough hair on top to cover. Attachments should stay hidden during movement, in a ponytail, and from the side.
The wrong quantity
Too little hair can leave a visible edge; too much puts unnecessary strain on the hair. Use the quantity advice and judge the result from several angles.
Rough edges after cutting
When the weft is divided, the cut points have to stay stable. If in doubt, have a trained partner do the trimming.