I've gotten a bunch of jobs over the years with the client's understanding that I don't know enough about something, but I will know what I need to know before I start billing. Long time clients have no problem with this and know three important things: (1)no one knows everything; (2) the narrower one's experience is, the more they have to charge; and (3) knowing 70% of the necessary information on a project in context is often worth a lot more than knowing 100% out of context. I try really hard to avoid clients who can't comprehend these three important things.
The last point is a bit obscure so I'll provide an example. I am not an electrical guy, it really does feel like PFM to me. I had a project that was presented as a compression project, but the key uncertainties were the electrical driver (VFD or not, how much over design, what voltage to use, etc.). The packager was going to supply the EE expertise, but my client wanted enough knowledge within the project to prevent the packager from taking an inappropriate direction because he didn't understand the process. I took the job and started trying to educate myself on the key tripping points. The EE had never worked with compression before and made a bunch of recommendations that were based on the load being a LOT more cyclical than it really was (he was looking at the numbers for a single throw recip compressor when he was dirving a flooded screw compressor). He and I spent a day together mostly talking about how the compressor worked and what was important for the load--he went back and made some major design changes (cut the cost by over 1/3). Without someone on the project who understood the application (context) and was knowledgeable enough to speak coherently (70% knowledge) with the subject-matter expert (who had extensive knowledge) we would have paid far too much for an application that probably would not have worked instead of paying much less for one of the best running compressors I've ever seen.
On the other hand, I've often taken jobs that felt like I didn't have enough mechanical knowledge to do successfully. For example, I'm very comfortable working in ASME B31.8 (gas pipelines), but ASME B31.3 (plants) is a foreign language to me. When a client decided to modify a compressor station that had been built to B31.8 (which is legitimate), but wanted the changes to comply with B31.3 (which isn't wrong) I told him I wasn't sure what the difference was, and that it would take me a bit of time to get up to speed, he might want to find a plant engineer to do the modification. He said that all of the plant engineers had a sense of urgency that was not aligned with the project needs and would rather pay me to get up to speed. It worked out fine and everyone was happy, but it only worked because of full disclosure.
David Simpson, PE
MuleShoe Engineering
"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.