Every now and then you go to a seminar which goes horribly wrong for the speaker. Someone asks a question that the speaker answers poorly or cannot answer. Then other people start asking questions or offering critical comments and it gets worse.....
Why does this happen? How can the speaker prevent it?
I think it may be because the speaker violates the important principle:
Never offer undefendable ground.
i.e. do not make claims that you cannot back up
Speakers will sometimes make claims that are not necessary for the actual talk but will irritate members of the audience, particulary senior people. I think students who "parrot" lines they have learnt from their advisor about justification for their work.
A random set of sample claims which you may hear variants of include:
-our results will allow the design of new materials
-silicon based electronics has no future
-density functional theory cannot described electronic correlation effects
-molecular dynamics simulations of biomolecules tell us nothing
-the Hubbard model oversimplifies the true Hamiltonian
-BEC's allow us to tune parameters in a manner that is not possible in traditional condensed matter systems
-quantum information processing is going to revolutionise computing
-our theory agrees with all the experimental results
-everyone elses theory is wrong
So if you don't want your talk to go pear shaped, don't claim anything you wont be able to defend.