Hairy Bittercress (Cardamine hirsuta) likes human intervention. It prefers places where the soil is tilled or worked, as a vegetable garden or a corn field after harvest. Its leaves are not bitter but slightly spicy, like Watercress (which, by the way, belongs to the same botanical family of Brassicaceae). When in winter the weather is soft during a week or more, it immediately starts growing leaves and flowers.
So this winter it flowers and grows all the time since November.
The little plants even got the occasion to grow bigger and to make fruits. The fruit is a siliqua much longer than the flowers.