Write a letter advising a hypothetical sole proprietor to choose another form of business ownership. By definition, a sole proprietorship is an unincorporated business owned by one person known as the sole proprietor. The majority of U.S. businesses are owned and operated as sole proprietorships. Write a letter to a hypothetical sole proprietor explaining why he or she should convert the sole proprietorship to another form of business ownership (for example, a traditional "C" corporation, an "S" corporation, or a limited liability company).

One example of a letter to a hypothetical sole proprietor could read as follows:
Dear Sir/Madam,
I have realized that you have been operating as a sole proprietor for quite some time now, and I have noticed that you have made significant progress within that period. For example, you managed to invest in real estate last year and acquired a vehicle to assist you with product delivery. As your attorney, I would like to tell you that it's time for you to change your business into a limited liability company.
Judging by the level of progress you've managed to achieve, it's safe to say that you need to protect all that you've gained. If you continue operating as a sole proprietor, you will be personally liable for any lawsuits that may affect your business. Since I know that you don't want to lose everything through a lawsuit, you should register your business as a limited liability firm so that any liabilities fall entirely on the business.
I hope that you consider my advice, since the earlier you do the conversion, the better.
Sincerely Yours,X
http://bloomlawfirm.com/articles/31/limited-liability-corporation-versus-sole-proprietorship

Here's an example of what your letter could look like to get you started:
Dear Business Owner:
While sole proprietorship affords a businessperson relative ease in the conduct of their affairs, usually requiring little to nothing in the form of paperwork or legal filings, the legal risks one assumes when operating as a sole proprietorship generally do not outweigh the minor inconvenience of organizing in another way, such as a limited liability company (LLC) or C corporation.
As a sole proprietor, you and the business exist as a single entity in the eyes of the law. Any error, omission, or liability incurred by the business is, therefore, yours as well. Should you have, for instance, an employee whose negligence causes injury to a customer, not only the assets of the business but also your personal assets (including your home, car, and other possessions) can be taken to fulfill a judgment against the business.
By contrast, operating as a LLC limits your liability. In the aforementioned scenario, only the business's assets would be exposed to seizure in fulfillment of a judgment. What's more, a LLC generally offers you the same accounting ease of "pass-through income" as a sole proprietorship, and organizing as a LLC can be done inexpensively and with no more than a few hours of investment.
I therefore advise you to reevaluate your decision to operate as a sole proprietorship and reorganize as a LLC.
https://www.entrepreneur.com/article/72134

When you write this letter, you should let the sole proprietor know that while establishing a sole propietorship costs nothing, this form of business does not provide legal advantages. If, on the other hand, the sole proprietor establishes an LLC, or limited liability company, he or she will only be liable for the amount he or she has invested into the business. In other words, as the owner of an LLC, he or she will not be personally liable for the business's losses. However, a sole proprietor can be held liable for the business's losses, and creditors can try to seize a sole proprietor's house, car, or other assets to reclaim losses.
In addition, an LLC can raise money more easily than a sole proprietorship can, as members of an LLC can sell membership interests in order to raise capital. An LLC can also more easily transfer ownership of a business to another party without disrupting the functioning of the business. On the other hand, a sole proprietor must sell each element of asset of the business separately, which is a far more cumbersome process.
Sole proprietors and sole members of an LLC must report their business income on their tax returns and keep track of their expenses. Therefore, the process of filing tax returns is similar for a sole proprietor and for the sole member of an LLC. While setting up an LLC costs about $1,000 and involves more paperwork than setting up a sole proprietorship does, the LLC can provide a great deal of protection for the member or members and is generally worth this one-time expense. 
https://www.legalzoom.com/knowledge/limited-liability-company/topic/llc-sole-proprietor-partnership-comparison