Oh well
haha
If you believe it is possible, go and practice it
if you don't think it is possible, then go learn some other new skill
10 years old skillset and people are still debating
(correction) in 2012, a very high profile coach from China told me (when I ask him what new technique are there now) and he explain to me of bh flick generating underspin.
If you make sure you only brush the lower part of the ball (below the mid point of the ball) and direction towards the lowest point of the ball, it is an underspin action.
Think pendulum underspin serve contact point on the ball
Now, i'm not here to debate. But to tell you, it is possible.
Not going to try and explain the above again.
The coach who taught me this, is very very high profile.
Chinese Super League coach: