We've all been there. A new client comes in and informs you that she'd like the longest and thickest lashes possible. Or, she shows you a picture of a girl who is clearly wearing high quality strip lashes and doesn't understand why you can't replicate that with extensions. Or the worst of all, a client demands that you put the longest and thickest lash possible on her because her "regular technician does it that way".
Never give into these people!
One of the main causes for severely damaged lashes comes from technicians using extensions that are much too heavy for the client's natural lashes. Inexperienced and improperly trained technicians might not realize the dangers of using such an extension at first, but when their client comes back with broken natural lashes, or over time experiences a deteriorating lash, they will learn their lesson (hopefully).
Look at it this way:
Picture a tree branch. Now picture a nice bird landing on that branch. The branch is now supporting the weight of that bird, but it's so light that it barely makes a difference. The branch is now accentuated by just the right amount.
Now picture that same branch, but instead of a bird, an elephant perches on it. The branch can't support the weight of this creature so the branch will either SNAP, off right away, or bend under the pressure, until it's no longer strong enough to hold, and eventually breaks.
This is the same with lashes!
When you apply an extension that is too heavy for someone's natural lash, their lashes are going to weaken and/or break under the weight. When your client has to start coming for more frequent fills, or worse-removes them and sees how weak they are-you're going to have to deal with a very angry client. Not only did they just spend a lot of money for a service that probably didn't even last a week, but they spent a lot of money to have their lashes destroyed until their next shed.