You're Correct!

To score well you need to know your yardages of all your clubs so that you can hit close to the flag and get your score as low as possible.

You may have a favourite club, a club you know you always hit well, or the club you practised with most when you first started playing. But it is really important to learn to develop the ability to play all of your golf clubs well, rather than to keep reaching for the club you like the most.

In order to score well you have got to know the yardages that you hit all of your golf clubs. When you go to the golf course and you are practising either on the driving range or out on the practise ground, work on practising with every club in your bag, not just your favourite 7 iron, or whichever club it happens to be for you. When you are out on the course, you need to know the yardage that you have for a particular shot and you need to know the right club to hit for that shot, rather than reaching for your favourite club all the time, which is not necessarily the right club to get you close to the flag.

When you go out on to the practise ground, work on using all of the odd number clubs in your bag on one practise session. Start off with your 5 iron or your 3 rescue and hit a shot with that, then hit the next shot with your 5 iron, then hit the next shot with your 7 iron, then the next shot with your 9 iron, so you are working all the way through those odd numbers. You can do it with your driver and your 3 wood as well and as you are hitting a shot with each club, take it out of your bag and then prop it up against the driving range bay divider, or leave it out of your bag, or prop it against your bag if you are on the practise ground.

Work on hitting all the clubs again, putting each club back into the bag so that you know you have hit all of your clubs and you will get used to hitting all of your clubs so you do not practise with just one club that becomes your favourite because you have got trust and belief in that club.

On your following practice session, do the same again with all the even number clubs to get used to using all of those clubs in your bag. Work out how far you hit them, so you know the yardages for each of them. The next time you are out on the course and you know how far it is to the flag, you can now pull the club out of your bag required for that particular yardage. You will know that you hit it in practise and you will now be able to score well because you will get the ball close to the flag.

Even though you might like your 7 iron and you know you never miss with it, it might not necessarily be the club for the task in hand. Work on developing the fact that you like that club into all of the other clubs in your bag so you do not have just one favourite club, they are all your favourites.

It is really important that you have good tempo when you are out on the golf course. If you start trying to force that 7 iron to go a yardage that you do not hit it, it physically will not go that distance. You are going to be swinging the club too hard, you are going to be off balance as you hit and you are not going to get a good strike from the centre of the club face.
Similarly, if you are swinging the club way too slowly because you are much closer than the distance that the 7 iron would normally go, the same thing will happen and you will mis-strike and become inconsistent.

Work on using all of the clubs in your bag and use all of them when you are out practising so that you can use all of them when you are out on the golf course with confidence, rather than just your favourite club.