In the Japanese business culture of 50 years ago, lifetime employment with a single company worked OK. However, business pressures have even led modern Japanese business to take this attitude: You can have the job until you don't want it any more OR until you can't do it any more OR until someone better and cheaper comes along.
Stating a goal of "lifetime employment" is unrealistic these days and as such, MIGHT even be taken as a negative factor in deciding to hire you.
In terms of your mental well-being, you want job security - but unless you join a strong labor union, that is unlikely to happen. For most modern business, the better attitude (to keep you sane) is to recognize that LIFE is uncertain and business is just a part of that life. Making a life-long commitment causes you to make your job so much of your life that you can easily neglect other parts of that life - like family and friends. You become what we in the USA call a "workaholic" - which means that you become morbidly addicted to your job. This is always a bad thing.
I eventually learned that to be mentally healthy, I had to remember that with regard to you and your employers, the books are re-balanced every time you get a paycheck. If times, situations, requirements, or your educational levels change, you owe it to yourself to be willing to escape deteriorating situations. Stating a goal of "life-long employment" might be true, but you don't want to state it outright. It makes you sound desperate, which is when the employer realizes he can EXPLOIT you rather than just EMPLOY you. I hope you understand the difference.