A more thorough explanation:

The lawyer-witness rule is a principle that states that an attorney who is likely to be called as a fact witness in a trial cannot participate as an advocate in the case. This is unless the testimony is about an uncontested matter or the amount of attorney's fees in the case. Disqualifying the attorney would create a substantial hardship for the client.

The rule allows an attorney who is actively participating in the case to be a witness on formal matters. However, it discourages testimony on other matters on behalf of a client.

For example, if a lawyer is representing a client in a personal injury case and was present during the accident, they may be called as a witness to testify about what they saw. In this case, the lawyer cannot continue to represent the client as an advocate in the case.

Another example is if a lawyer is representing a client in a contract dispute and drafted the contract in question. If the lawyer's interpretation of the contract is in dispute, they cannot continue to represent the client as an advocate in the case.

These examples illustrate how the lawyer-witness rule prevents a conflict of interest and ensures that the client's best interests are protected.