So here's the deal. Your lash artist can only lash pre-existing natural lashes. What does that mean for you? Something that you see in a picture may not be achievable, no matter how exact the styling is followed.
You can't change your genetics, hormones, or your age, these all have an influence on the quantity and quality of your natural eyelashes. Generally speaking, younger people tend to have thicker, fuller natural lashes.
If you're struggling with thin and brittle lashes, there are a few things you can do to improve your lashes. Make sure you are taking a multivitamin at the very least. Hair and nail and collagen supplements are an extra boost. Avoid waterproof mascara and being rough when removing makeup. Lash curlers are a no-no! Find a good lash serum, your lash artist can assist you with that.
This is an example of why your results may vary. Both of these ladies got the same classic lashes, but they had very different natural lashes to begin with.
At the end of the day, having realistic expectations of what lash extensions can do for you, and taking care of your natural lashes will give you the best results.