One of my teachers said "the heart is not a pink cloud, it can be like shattered glass." Ancients compared it to a "flaming sword of truth." Opening the heart may bring agony, confusion, and tears, but gives way to joy, love and a boundless experience of unity.
The work of opening the heart is hard work. It will break again and again until it makes its final opening. Awakened people testify that it is worth it. Many seekers don't like it though, and stick to grasping concepts, perhaps awakening half-way to an isolating experience that is disconnected from things, and missing love.
Working on the heart can be done almost 24/7. I discovered that mostly on my own, with a little help from teachers or books, finding that by being receptive and mindful of everything arising in my present awareness, I could do the hard work of acceptance. It can be done by intent, and doesn't need to be by grace, blessing, or good luck.
I t is difficult to maintain a practice of acceptance 24/7 but its like anything else that takes effort. We just keep getting back up after the falls. Attending to inner conflict is tedious, more for some than others. It can be unsettling yet can be done while fully engaged with life and not requiring lengthy retreats or monasteries.
The heart must accept the knowable. All of it. Now, nothing arises in my awareness that I can't accept. That means that I never feel as though something is missing or that something is here that shouldn't be. Because of this, the most important blessing of all is that my inner critic and judger have been silenced. I have questioned many who are considered awakened, and it is their experience too.