This requirement is simple enough as stated. However, personal knowledge may not be assumed. This means that the lawyer must establish by testimony that the witness has personal knowledge before the witness can testify to what he or she experienced. Thus, a witness called to testify to seeing a robber in a hotel lobby will first have to be asked questions that show that the witness was in the lobby of the hotel and was able to see what was going on there. This requirement, like exhibits, is another instance of the examiner having to "lay a foundation" for the witness' testimony. While all this may seem simple in the abstract, it is a•roblem for many lawyers, because there is a natural tendency in people who know the facts of a case well to forget that other people do not share that knowledge.