Doing a standard course on a part-time basis can be tricky for service personnel on active duty, explains flight sergeant Chris MacKay, who worked with Anglia Ruskin to get the first 21 RAF medics enrolled.
The unlucky ones found it trickier to service their mortgages.
What's trickier for service organizations, though, is the difficulty of measuring quick, tangible results.
Djokovic, the No. 3 seed, was the predictable winner in this third-round match, prevailing, 6-1, 7-6 (4), 6-3, and showing plenty of poise in a situation in which the crowd was ready to lift Blake and when the gusts were transforming easy shots into tricky ones and service tosses into adventures.
Numbers are tricky for any service, specifically Google+.
The airlines, plus Thomson and Thomas Cook, have joined a dispute resolution service for tricky complaints that cannot be resolved by the companies themselves.
This can make for tricky driving; the park service constantly reminds visitors not to brake suddenly if they spot an eagle and to be mindful of traffic if they decide to pull off to the side of the road.
But collecting tax on services is tricky, and e-commerce can only make it harder.
The experience of managing the company through launching controversial services is tricky, but I can only imagine it would be even more difficult if we had a public stock price bouncing around.
Greater diversity in providers and technological disruptions to viewing models will also make a single levy for services trickier to defend.
