Achievements do not guarantee happiness
This is the Self calling you back to the source. What people achieve in the world will only last for a short period of time. Not only that, their achievements cannot guarantee their happiness. That's because achievement cannot provide what it doesn't have. Happiness comes from the inside, the place where you actually experience it, not from what you achieve.
Stress comes when you are afraid of failing. Now you can't always control if you succeed or fail, but you can always abide in the peace and happiness that's at your core.
Where do you experience happiness
So when you feel happy and at peace, meditate on where you actually experience this happiness. Does it come from the world and what you see, or does it come from what you are?
Peace is closer than a state of mind
And when you feel tense and stressed out know that peace is not far away. You can find this peace faster than you can change your mind. That's because peace is not a state of mind. You are not trying to get your mind just right. That's an endless task. Awareness is the source of this peace. The very fact that you are Aware of the stress means that you are free of it, not caught in its grip.
So meditate like this: When you are happy and at peace, note where you actually experience this happiness and peace. And when you are stressed out, notice that you are Awareness and not a state of mind. Stand here and see if stress can really bother you.
The nice thing about this meditation is that you can do it all of the time, whether sitting, standing, walking or lying down. It does not require any particular posture. Still spend some time meditating on what's really important.