I say that because it's an important thing to keep during the process. Several times recently I've seen posts by agents that have been painted, in the comments at least, to be examples of "agents behaving badly." But really, all of this agent/client animosity is not only disheartening, it's also completely avoidable if you have the right mindset and act appropriately. If the clients in these examples (no, I'm not going to link them) acted like professionals, then the agents would never had cause to get upset in the first place. There is a way to avoid the drama and even succeed, and it starts with understanding the agent/client relationship.
According to Merriam Webster, an agent is "one who is authorized to act for or in the place of another: as a representative, emissary, or official." A client is "a person who engages the professional advice or services of another."
So what does that mean in plain English? The agent works for the client. When you're sending the query letter, you're not applying for a job. You're recruiting.
Now, don't let that go to your head. You are recruiting someone who is talented and in demand. You're a headhunter, and the person you are seeking has other offers. You want to make a good impression on them. You want them to choose you.
Think of them as Harvard graduates (and some of them actually are), and you're a medium-sized paper company from Pennsylvania. How do you get them to take the job? You do it by showing them why they should want to work for you.
But that doesn't mean you beg. There are lines between persistence, pestering, and pathetic. Try to avoid crossing into pestering, and steer far clear of pathetic. If the agent doesn't like your work or won't respond, move on. If they really like your work, they'll let you know. This waiting a year for a response stuff is ridiculous.
The key in the end is to be professional. Treat them with respect, and they should treat you with respect. If they don't, then you don't want them working for you. Write them off and move on.
Keep your dignity. If you've written a great novel, then you can only try to help them see it. If they don't, then they aren't the person you want working for you.