If you live in a cold winter climate like I do, this is one of the toughest times of the year. It's easy to make excuses when it comes to staying inside.
And if you're a solopreneur or simply work from home generally, this can be dangerous. You can go days if not weeks (seriously) without leaving the house. Usually when I leave the house, it's just to go somewhere quickly in the car.
Getting outside is good for both your mental and physical health. You get some steps in, you get some fresh air, and you're exposed to a new environment. You may even be inspired with new ideas.
Make a conscious effort to get outside. If you have a good day of weather, take advantage of it. But even if it's cold, it's always going to be cold. Don't let it be an excuse.