Since there are four dharmas simultaenously operating and no guarantee that people will make the right choice, ups and downs in the course of over-all Dharma are inevitable. However the cosmos is fitted with a self-correcting mechanism. This 'mechanism' is explained in the key shloka 7 of Canto IV, a shloka that most Hindus know by heart and are prone to repeat whenever they feel that things are falling apart, as if it were some kind of magic panacea : ' When Dharma declines, and adharma flourishes, I give myself birth, to restore the balance.' Divinity is not born; only creatures caught in the coils of karma get born and re-born. Divinity gives itself birth as and when required. The implication is that, just as there is Krishna present to console, advise and inspire Arjuna, his devotee (bhakta) and friend (sakha), so there is always a divine presence for anyone ready to receive spiritual guidance. Knock -- and the door opens.
The important thing is to realise that all action must be treated as 'ritual' (yajna) and not sensual. In ritual action, selflessness, dedication and sacrifice are of the essence. All action is service, but not to oneself. The concept of service purifies action of selfishness. This liberates the doer from the hell brought by ill karma, and equally from the heaven of good karma. Both heaven and hell are seen in Hinduism as temporary after-life punishments for ill deeds and good deeds. The secret is to see inaction in action ('ritual' unself-concious action brings no fruits, good or bad); and action in inaction ('selfish' knowledge brings fruits, good or bad).