An open mind is become one of the most important mindsets to possess in this century, with the rate at which change is occurring one cannot develop unnecessary attachments to ideologies or comfort zones, "I'm just lazy" isn't a really good excuse for anything these days. I've had people tell me that the reason why they're not being promoted at work is because they're not computer savvy, they'd say it with such a note of finality that all I respond with is a polite smile.
The world of software engineering is bedeviled with rapid pace of innovation, it is easy to develop hubris as a result of success with one's current stack (language or framework of choice) however one should heap attention on the happenings around the sector or one's stack can be deprecated overnight. There are those who are too cautious and never pivot and there are those who are too anxious and pivot so much they're hardly anywhere, the trick is fighting that sweet spot between fear and hubris.
Once you've gotten depth in one language you need to be able to explore others that compliment what you know. Imagine if one learnt html without css or Javascript, weird right? Well that's how weird it is when you go years without learning (even at surface level) any new languages.