Problems
I had used normal keyholder for my keys. But there were several issues I was frustrated by.
Absence of pockets for women
For women, it's lucky if a clothing you bought has a pocket. When they do have pockets I would say most of they have very shallow pockets or they're just a decoration. These days, more and more women's clothes have pockets, but I often thrifts vintage clothings. And it's rare that those old clothings have big enough pockets. Why don't you carry them in a bag? It's also annoying because you have to search the keys in the whole bag. Taking it out is one another task we don't need.

And then, in The Netherlands, we bike
In The Netherlands, as you know, we bike a lot. So it's important that your hands are free. But not only for biking, you want to have your hands-free when you want to carry big grocery bags, or when you receive/bring your big parcel from/to a post office. Especially when you don't have functional pockets, where can you put your keys away?

No pretty key neckalces
There are more and more key neckalces in the market, but I didn't fancy any of them. They're either by a luxury-brand made with high quality leather, or by young brands made with parachute cords.

Inflexible length
Those that are on the market, I also didn't like them as they lack the flexibility in changing the length of the key necklace.
Material hunting
After feeling those concerns for long, I already had some ideas of what my new key necklace could look like in my head. So I decided to go and find materials.
I found the type of cords I'd love to use, so I purchased some different colours together with other materials.
Ta da✨
I first made a prototype, but it all went well, so I continued creating 2 more with different colours. The prototype is the one I still use daily.
With 2 fisherman knots, you can adjust the length of the necklace.

Wearing them as marketing
As I was chuffed with my new key necklace, I started to use this daily. My colleague saw this and she asked me to make one with her colour. I also gifted one to my friend, too.
Learnings

Problem thinking
Although I didn't have actual evidence to illustrate my design process since it was all in my head, I realized the significant value of problem-centred thinking. It makes the while process of building a product so much easier. Through this experience, I truly appreciated the strength of this approach.