Minnesota requires expert testimony to prove certain parts of specific claims. Not everyone is of proper training or experience to, for example, determine the value of real estate or quantify the amount of money a failed mortgage refinance may have cost the borrower.
The retention of your expert calls into play a series of requirements. The first is a written report on the expert's background research and opinions. In some instances the expert provides conclusions, but most correctly the expert renders an opinion. The retained expert must also prepare his or her CV, disclose prior expert testimony, and their compensation for their work.
Even if you prove every other element of your claim, if you don't prove damages, you don't get compensated. Knowing when you need an expert and what the expert's background is are both critical to your case. In the best scenarios, the lawyer is taking the lead from the expert on what the expert wants or needs to see, there is communication on the shortcomings of the case, and there are authorities to support the basis of the expert's opinions.
Don't think all people can testify on all subjects. Be aware of when an expert is needed. You don't want to lose out on a good case because of a fundamental error like this.