Nail plates do not have sebaceous glands (that which produces oil) and therefor are not 'oily'.
Old wive's tale spouted by a tech bewildered at why the product won't adhere.
Some people are not compatible, no matter what you try. (I've personally met 2 people such as this)
They could be serial pickers, but you can't catch them.
They could be taking medications that are contra-indicative.
They could be using products to clean their home, or working with products that cause issue...
They could have health issues (menopausal, thyroid....)
There are any number of reasons why a product may not stick (aside from poor prep etc).
In most cases, you can play around and find what works for 'that' client.
Changing systems, changing bonding methods (from acid primer to non-acid primer, etc...) Wet prep to dry prep.....
A teensy-weensy bit of extra filing/etching of the nail plate on the rare client.
There is no sure-fire answer, all you can do is 'try' and see what works and what doesn't.
hth's
