"It can be overwhelming encountering the effort and commitment people give to Macmillan," he says. "I think people get sentimental about the charity because in a world where so many charities are changing so quickly, we've managed to keep hold of a tradition of caring that has remained constant."
Cardy has spent most of his working life in the health and medical field.
As the chief executive of the MS Society he drove the charity through one of its formative periods and succeeded in getting MS medication on the NHS.
"In all three of my jobs in the charity health and disease field I've been frustrated by how hard it is to bring about change in health services," he says. "But the thing to always remember is that change is possible, and unconstrained self-funded charities have the power to play a big role in this."
Macmillan is a fundraising organisation in its truest form. Cardy is resolute that it maintains its independence by generating income through public channels without reliance on statutory grants.
"We completely dictate our agenda and to maintain the trust that we inspire it's vital that we hold on to this autonomy," he says.
Cardy is a true believer in the benefits of maintaining a critical voice.
At a time when more voluntary organisations are entering into paid contracts he thinks that charities should take care to hold on to their original purpose.
"One of the things that marks charities out is the mindset and mission of the people who set them up, and it's often difficult to keep those objectives strong to ensure they don't fade with time," he muses.
"Unfortunately, once you take on contracts and become beholden to another authority it's easy to become confused about which side of the fence you belong."
He is sceptical about some of the proposals for a new charities bill that, if implemented, will see far stricter government regulation of charities management and accounting procedures.
"There is an inability of government to recognise the boundaries of its own business," he says. "Any political party that comes into power can't help themselves from trying to step in and regulate what they can't control, and this governing party is no different. Trying to generate something like a Standard Information Return for such a diverse sector will lead nowhere but down a path of enforced uniformity which won't work."
Cardy is dismissive of the argument that there are too many charities working for similar causes, and regards the scope and scale of organisations within the sector as a healthy and valuable state of affairs.
"The proliferation of cancer charities in particular is always represented as a bad thing," he observes. "But if you take a walk down a busy high street you don't hear people complaining that there are too many shops selling similar things. People like it that there are different brands with different packaging so they can pick which is best for them."
He thinks the cost and pain of large-scale mergers outweighs the benefits of such a consolidation of resources. Instead, he argues that the future of the sector lies in solid and practical alliances and partnerships based on common purpose.
"Not long ago, cancer was still a taboo topic, but this is gradually changing and I think charities have played a part in this," he said. "But different people respond to different approaches and messages."
Cardy is critical of charities that rely on the 'fear factor' in advertising and use hard-hitting dark imagery in order to make their point.
"The whole philosophy of scaring people into giving disturbs me," he says. "Going for the fear factors may induce some people to give, but you also run the risk of inducing terror among the very people you're supposed to be helping. We've got the tabloid newspapers to do that for us."
He believes that public campaigns should reflect concern for the cause they work towards and the people that are affected by it.
"As chief executive at the Motor Neuron Association I learnt a very valuable lesson - that you shouldn't add to people's burdens. As a charity you are speaking as much to your beneficiaries as to the people you want to give you money. But your main responsibility is to the people you're working for."
As an agnostic, Cardy believes we have a duty to leave the world a better place than when we found it and finds his role at Macmillan lets him make a difference.
"This is the only world of which we can be certain and I really believe that the work we do at Macmillan touches people's lives," he says. "It's my responsibility to do the best I can for them."