How can we be good Muslims if we cannot practice all our duties?

Praise be to Allah, the Lord of the World; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

Islam renders a set of actions that help a Muslim who is delinquent in performing all Sharia duties and tasks. Such actions are laid down to encourage one to be steady on the Divine way of life. Among these actions are:
1) Knowledge.
No doubt, knowledge induces fear of Allah in ourselves.
Allah Says (interpretation of meaning): {… who have knowledge among His slaves that fear Allâh. …} [35: 28].
2) Putting knowledge into practice.
A good deed leads to its like and induces a new light in a doer's heart.
3) Invitation to Allah.
Inviting others to Allah's way of life, and the desire to bring people to His way can help one be steadfast on the right path. If one thinks that he is an exemplar, this will lead him to be better and to do right.
4) Patience.
A person, who recognizes that adherence to the teachings of Islam is the only way to the everlasting happiness, will be patient. A person who takes patience for the sake of worldly matters will find it worthier to be patient for the sake of matters that will lead him to Paradise.
5) Death, the Hell-Fire, the Paradise.
One has to remind himself of death, Day of Judgment, and that he does not know his final fate: the Hell-Fire or the paradise.
6) Allah's Help.
One has to seek Allah's Help, has to supplicate Him for forgiveness, has to know that there is no power nor might but of Allah.
7) Good Association.
Associating with good people and avoiding company of bad people is very important, since a friend may have good or bad influence on his friend.
Allah knows best.