Don't trust the difficulty rating shown by TT. It is not accurate in my view. For example, I come across many keywords where the 0ff-site SEO is very weak. I mean the sites which are ranking in the first page hardly have any backlinks, but they are all pretty good in on-site SEO. Keywords is there in Title, desc, H1 tag and URL. In this case, TT shows the difficulty rating as difficult and above, but in reality I can reach the first page pretty easily. Keyword research is something which needs to be done manually for higher success rate. If you rely on tools completely which lacks human intelligence, you will be mis-guided for sure!