Professional pride means that I pay a high degree of attention to detail in all of my work, but in professional engineering practice, there are multiple safeguards against error, based on an acceptance that the very best work has a few percent of errors. Expert witness work is an individual rather than a collective activity, so it does not have these safeguards, which means that you have to be your own QA department.
No expert would enjoy having errors in their arguments or calculations discovered in cross examination, and in the UK, expert witnesses are not immune from being sued by aggrieved ex-clients who feel they were led into an overly optimistic view of their prospects by an expert witness they had engaged.
The expert therefore needs to be very careful in what they say and write, even at the earliest stages of engagement. They should resist any urges they may experience to sell the client on using their services by being the most expert who is most optimistic about their chances in court in the beauty parade which larger law firms use often nowadays.
Similarly, the expert witness needs to be careful about their terms of engagement. Professional Indemnity Insurance does not necessarily cover every possible set of terms an expert might sign up for, and some law firms have a surprisingly bad track record of paying their expert witnesses on time.