Checkmate in two moves more leads to a "Puzzle Failed"

Unfortunately there are some bad puzzles on lichess. It limits our ability to benefit from the chess puzzles. This has been mentioned many times before (for example: http://en.lichess.org/forum/lichess-feedback/extremely-specific-chess-problems). It is also unfortunate that bad puzzles often even have a good feedback score. I often lose as many points on one bad puzzle as I win on ten normal puzzles. Sometimes I play what I think the website wants, but often I just play what I think should be accepted as correct.

I think everything is fine like it is. Find the fastest most forcing - the best move. This is the training. Learn to calculate. If you are not able to research the right combination you didnt find the best move combination. I failed many times, but is ok.

"This is a good move find a better one" is not important. Is a last chance after you failed. I dont know how these puzzles are generated. Maybe if engine says best move is only 0.3 stronger.. give it a "This is a good move..." But we don't have to care if the "this is a good move..." is right or wrong used, because in these puzzles is only one really thing to do for you:"FIND THE BEST MOVE"

#12 Agree 100%

I agree with the OP, I think this is a valid concern. I think there is little practical reason to prefer one forced mating sequence over another, and both should be considered equally valid.

"...it is the main goal to check mate in the fastest way"

When did this ever become a goal, and why should it be one?

I think possibly there is some confusion between the ideas of being "fastest" and "most forcing". Forcing variations are generally the fastest, but in this case both variations are equally forcing.

I think we need examples to know what we are talking about.

I just "solved"a puzzle. My first way was a this:

1. a check only one move to react
2. a check only one move to react
3. a check only one move to react
4. a checkmate

and it was a "good move but you can find a better one".
After some time I found a better solution and I'm thankful because it remembered me to a trick (a small triangel movement) which can be used from me surely in some other tactical situaitons.
The right solution was:

1. a check only one move to react
2. a check two moves are possible to react
3. a checkmate (the same move for me fort both last moves)

If my "good move" answer finished the puzzle I missed a trick I didn't see. I htink nearly everytime you get a "good move" there is a chance to learn the "new trick".

I'm not convinced this is a good reason to disallow an equally valid solution. If the "trick" you learned is really of any importance, it will appear in another puzzle as the only forcing solution.

Sputnik Monroe This is a good point, however the problem is often the puzzle will be failed if you play a variation that takes longer. In your example you got the "good move but you can do better" response which I think is a good system because as you said knowing the quickest checkmate is helpful, however I don't think that you should fail the puzzle for finding a longer checkmate.

Sputnik_Monroe I understand that it is about improving calculation, however when you fail a puzzle after finding a solution that does in fact checkmate the feedback you get is "I should have calculated for longer to try and checkmate faster", however this mentality is a complete waste of time. The reason I play chess puzzles is to try and find key ideas or tactical themes. If I have found a solution I already have found these themes, yet the way the system is currently set up I then have to waste my time trying to see if I can checkmate more efficiently, and I believe this to be a waste of time because, as I said, I solve puzzles to try and get a better feel for tactical combinations / themes.

To clarify #18 was in reply to #16 and #19 was in reply to #12