In the A1 writing challenge "Learning the guitar" the question
"because I find that it's a soothing instrument"
suggests the answer
"car je trouve cet instrument apaisant."
which I can see is very elegant but why is my answer incorrect:
"car je la trouve d'être un instrument apaisant"
I can find other examples on the web of similar usage such this:
"...que nous avons trouvé d'être un trait distinctif..."