It may well be that you have agreed with yourself on an ultimate goal, but you must keep that to yourself. Ultimatums and threats do not work in a salary negotiation - and not at all if they are empty threats. If you are willing to put your words into action and actually resign, you can easily do so on the grounds that your salary does not match your skills - but do so in a different situation than during the salary negotiation itself.
Instead of ultimate demands or empty threats you can set a goal for yourself and make a plan for what you will do if you do not achieve the goal. For example, it could be asking for extra days off or paid continuing education as alternatives to salary increases.
Emotions and drama do not pave the way to a pay rise. Therefore, you should not say that you lose sleep at night or "Well, you promised last year..." as these are emotional and not factual arguments. A good and undramatic atmosphere in the room is crucial for a good dialogue where your manager listens to you - and vice versa, you should also listen to your manager.
At the same time, don't rely on the good vibes alone and think you can get a pay rise on charm and a good chat alone.
The constructive atmosphere and dialogue must be maintained until the very last minute, which is why you should not sigh demonstratively and slam the door on your way out.
Instead of using emotions, you should be as objective as possible, and perhaps even more so than usual with your manager. Think of it this way: salary negotiation is a specific type of conversation with its own dramaturgy and possible lines, which you need to rehearse thoroughly so that you can stick to the script and not improvise if you get emotional.
And if you are really sleepless at night, that concerns your well-being. If you're worried you might be suffering from stress, there is help to get.
Find out what to do if you are experiencing stress symptoms
Injustice can be a big driver for asking for a higher salary. But you're putting yourself at a disadvantage if you flaunt the feeling of unfairness. While you may not want to belittle your colleague, you are engaging in un-collegial behaviour and using an unsubstantiated argument that says nothing about your own contribution to the company.
You may have read that pay transparency in the workplace can be a way to increase pay - and that's true. But don't confuse this with talking about your colleagues' pay in your individual salary negotiation. Openness about pay is a collective means of strengthening your position in salary negotiations - read how you can achieve pay transparency in your workplace
Instead of looking at your colleagues' salaries, you can use IDA's salary statistics, which give an indication of your market value. Prepare a few strong arguments to support your value.
You cannot use your seniority as an argument in favour of a higher salary. If you want to use your years of experience, you need to show how your experience brings a particular value to the workplace.
It also belongs to the category of bad facts to say "I didn't get a salary supplement last year either". Nor can you argue that you were not satisfied with the salary you received when you started your job. That race is over and cannot be used as an argument in a current salary negotiation.
Instead, you should prepare a series of good arguments for the pay rise. Make a list of your successes and tasks over the past year and put them into perspective with the company's goals. And of course, don't accept if your manager rejects your request for a pay rise with bad facts like "you got one last year" or "you haven't been here very long".
See examples of good arguments for the salary negotiation
Your unpaid bills, your dream of a holiday home or your son's after-school activities don't interest your manager in a salary negotiation. It may be personal matters that motivate you to go the extra mile in a salary negotiation, but you should keep those to yourself.
Instead, your tight financial situation should motivate you to prepare well for the salary negotiation. Preparation is crucial. Don't expect your manager to have a clear overview of your tasks. Your diligence and high level of responsibility do not speak for themselves - you need to articulate how you add value to the workplace.