With most companies, it isn't the product or service itself that makes them successful -- it is their intellectual property and how the company protects it. A trademark is one of the most important parts of the business's intellectual property, because it establishes your certified brand and it conveys to the people that your business, your product, and your services are legitimate and trustworthy.
Now, some companies may try to pilfer that goodwill and expertise by making their company confusing similar. They could make a product that look like your product, or, in the case of a trademark infringement lawsuit, another company may try to use similar logos or names to your company.
This can obviously cause some confusion among customers and it can tarnish your brand. But even if you may think that one company is infringing on your trademark, it is important to note the scope of the alleged infringement and the specifics of the alleged infringement. For example, does your company and the offending company work in the same industry? If not, then customers may not be confused by a similar name or logo. What if your company operates in a specific state, while the offending company doesn't? Again, this is unlikely to constitute confusion among customers.
If your company's name is trademarked, then the whole point of that trademark is to prevent customer confusion. Proving that customer confusion exists (or the premise of it) based on the actions of another company is crucial to any trademark infringement lawsuit.